Spectators watch a Russian "Buk" missile system being driven during the "Russia Arms Expo 2013" 9th international exhibition of arms, military equipment and ammunition, in the Urals city of Nizhny Tagil, September 25, 2013. REUTERS/Sergei Karpukhin (RUSSIA - Tags: MILITARY) - RTX13Z2M

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Pro-separatist Ukrainian rebels likely did not have the lone technical capability to shoot down the Malaysia Airlines Boeing 777 passenger jet that went down in a conflict zone close to the Russian border Thursday, according to a ranking Pentagon official.

“Shoulder fired missiles have a ceiling of about 10,000 feet. The Malaysian air flight was supposedly shot down at 33,000 feet. That means it would have had to have been shot down by either a sophisticated surface-to-air missile or an air-to-air missile fired by a jet,” the official, who was not permitted to speak publicly, told The Daily Caller.

Flight MH17 was en route from Amsterdam to Kuala Lumpur with 280 passengers and 15 crew members when the airline lost contact with the jet in Ukrainian air space. Ukrainian officials report the plane was shot down by a Russian-made SA-17 Buk truck-mounted surface-to-air missile launcher.

According to the official, both Ukraine and Russia have Buks, but since the plane was traveling from west to east and had already overflown all of western Ukraine, it’s unlikely the Ukrainian government waited until it reached the Russian border to shoot it down if it was perceived as a threat.

“The issue is that the type of missile battery that would have been used — if in fact, it was shot down by a surface-to-air missile — is incredibly advanced,” the official said. “It would have to have been provided by a state military like Russia. It also would have taken a well trained crew to use the system, so either a Russian unit working under cover or a rebel unit with Russian army advisors would most likely be the culprits.”

The possibility remains that a small unit defected and shot down the plane, but in either case it’s “most likely” the weapon responsible was given to rebels or used by the Russian military.

“If true then Russia should be held accountable,” the official said. “The Russians are smarter than to shoot down a civilian airliner, so if it was them it was a mistake, or more than likely it was rebels who didn’t know any better or didn’t listen.”

The governments of Ukraine, Russia and separatist leader Andrei Purgin have all denied responsibility for the shoot-down. Purgin told the Associated Press he was unsure if rebel forces even had Buks, and said that even if they did, they would be incapable of operating them.